dash a/c on max air {recirculate} no outside fresh air ?
all roof vents closed ?
what about brake and gas pedals, any outside hot air comming in there
any opening to the outside that allows hot outside air in while driving will pressurize the RV and push your cool air out thru any vents or windows that do not close tightly
two roof top a/c or just one
for (2) close front vent of roof a/c vent let it blow cool air back toward the middle
dash a/c can cool the front seats
its possible you might have to seal the roof a/c with some alu duct tape